1. Field of the Invention
The present invention relates to an epicyclic gear for high ratio reduction of the output rotational speed of a high-speed machine such as a gas-turbine, and as an increaser for stepping up the output rotational speed of a low-speed machine such as a motor, and having a suitable lubricating mechanism.
2. Description of the Related Art
Patent Specification of Japanese Patent Laid-open No. 1(1989)-288652 describes an epicyclic gear 700 in which it is possible to enlarge the reduction ratio or the increase ratio without interference of the planetaries as in epicyclics in which the pinion 701 and the internal gear 702 are engaged with three planetary gears 703, 704 and 705 in a single plane. It is shown in FIG. 8. When the ratio between the pinion 701 and the internal gear 702 is as high as 17 to 1, the epicyclic gear 700 has to incorporate at least two stages 706, 707 in order to prevent interference as shown in FIG. 9.
As a result, the epicyclic gear 700 has to be enlarged and the mechanical efficiency is negative by the increase in the number of gears. If only two planetary gears are engaged with the pinion and the internal gear, the epicyclic gear does not have the above drawbacks. However, the support of the pinion due to the engaging portion between the pinion and the planetary gear and the support of the internal gear due to the engaging portion between the internal gear and the planetary gears becomes unstable. An unbalanced load is apt to operate on each bearing supporting the pinion and the internal gear, and there is a danger of damage to the bearings at an early stage.
On the other hand, in pressure or forced lubrication, engaging portions of gears are lubricated by the supply of oil from a pump via an oil-jet. In oil bath lubrication, a part of a gear is steeped in oil which is stored in the casing, and the engaging portions of the gears are lubricated by the rotation of the gears.
In forced lubrication, the cooling efficiency is high and it is possible to lubricate the engaging portions of gears precisely. In an epicyclic gear as disclosed in Patent Specification of Japanese Patent Laid-open No. 1(1989)-288652, the oil passage is complicated and it is difficult to arrange the oil-jet at the most suitable position. Therefore, oil bath lubrication is adopted for gears of this kind.
Since it is not possible to limit the quantity of oil to that which is required to lubricate the engaging portions of the gears, the cooling efficiency of oil bath lubrication type is low. Also the mechanical efficiency of the gear is lowered by the mixing loss of the oil. Furthermore, depending on the structure of gears, there is a possibility that the engaging portions of the gears are not fully lubricated, and there is a danger of generating a partial discontinuity of the oil film in the engaging portions. At high rotational speeds, the oil is splashed outward by centrifugal forces, and there is a danger of generating a discontinuity of the oil film in the engaging portions at the center.